Organopolysiloxane emulsions are useful as parting agents for synthetic resins, rubber, paper and molds, coating agents on synthetic resin films and sheets and paper, water-repellents, softeners or lubricating agents for organic fibers (e.g., natural fibers and synthetic fibers) and inorganic fibers (e.g., glass fibers), emulsion paint, and anti-foaming agents. Of these organopolysiloxane emulsions, those emulsions of a small particle size prepared by emulsion polymerization are sometimes preferred from the considerations of stability and a high degree of polymerization. Such emulsion polymerized products are prepared by various methods. For example, JP-B 34-2041 discloses polymerization using strong acids or strong alkalis as the polymerization catalyst. JP-B 41-13995, Belgian Patent No. 686812 and U.S. Pat. No. 3,360,491 disclose polymerization using alkylbenzene sulfonic acids, alkyl-naphthalene sulfonic acids, aliphatic sulfonic acids, silylalkylsulfonic acids, aliphatically-substituted diphenyl ether sulfonic acids or alkylhydrogensulfates as the polymerization catalyst. JP-B 54-19440 discloses a polymerization process involving emulsifying and dispersing an oligomer of diorganosiloxane (consisting of 3 to 6 monomer units) in a salt type surfactant aqueous solution, adding an ion exchange resin to the dispersion, and effecting ion exchange of the salt type surfactant. Since all these processes take a long time for polymerization, a rapid process is desired.